This project studies the ability of rhesus monkeys and humans to detect small changes in innocuous warm pulses and noxious heat pulses applied to the face and evaluates the ability of medullary dorsal horn thermally sensitive neurons in the monkey to detect the same small temperature changes. This project also investigates the influence of attention on thermal discriminative capacity. A signal correctly indicating the location or modality of a subsequent thermal change improves detection performance while an incorrect signal worsens performance. Consequently, attentional factors may influence the perception of and response to oro-facial pain.